Aircraft Systems
Learn how aircraft engines, fuel systems, electrical systems, and flight instruments work — and what to do when they don't.
Overview
Understanding aircraft systems is essential for safe operation and troubleshooting in flight. This area covers the major systems in a typical training aircraft: the reciprocating engine, fuel system, oil system, electrical system, pitot-static instruments, gyroscopic instruments, and the magnetic compass.
Why This Matters
When something goes wrong in the air, you need to understand what failed and what to do about it. Systems knowledge enables rapid diagnosis and proper response to malfunctions. The FAA tests this to ensure pilots understand their aircraft at a fundamental level.
Exam Weight
Expected Questions
5-8 questions
Difficulty
Moderate
Notes
Expect questions on pitot-static instruments, carburetor icing, electrical failures, and which instruments fail with specific system losses.
Key Concepts
The 6 essential concepts you need to understand for this topic.
Pitot-Static System
The pitot tube measures ram air pressure (for airspeed). Static ports measure ambient pressure (for altimeter, vertical speed indicator, and airspeed indicator). If the pitot tube ices over, only the airspeed indicator is affected. If static ports are blocked, all three instruments give erroneous readings.
Gyroscopic Instruments
The attitude indicator and heading indicator are typically vacuum-driven. The turn coordinator is typically electrically driven. If the vacuum system fails, you lose the attitude indicator and heading indicator but keep the turn coordinator.
Carburetor Icing
Carburetor icing occurs when fuel vaporization and venturi effect cool air below the dewpoint, forming ice that restricts airflow. The first indication is a drop in RPM (fixed-pitch prop). Apply full carburetor heat at the first sign — expect a brief RPM drop as ice melts.
Fuel System
Most training aircraft use gravity-fed fuel systems with left, right, and both tank selections. Always use the appropriate tank for the phase of flight. Know the difference between 100LL (avgas, blue) and autogas. Never mix fuel types unless specifically approved.
Electrical System
The alternator charges the battery and powers electrical systems in flight. The battery provides power for starting and backup if the alternator fails. If the alternator fails, shed non-essential electrical loads and plan to land soon — the battery has limited capacity.
Magnetic Compass Errors
The compass exhibits acceleration errors (ANDS: Accelerate North, Decelerate South) and turning errors (the compass leads turns in the south, lags in the north). On east/west headings, acceleration errors are most pronounced; on north/south headings, turning errors are most pronounced.
Common Mistakes
Confusing which instruments fail with a pitot blockage vs. a static blockage — pitot affects only the ASI; static affects ASI, altimeter, and VSI.
Forgetting that the turn coordinator is electrically driven while the attitude indicator is vacuum-driven — they're independent backup systems.
Not applying carburetor heat soon enough — by the time RPM drops significantly, substantial ice may have built up.
Mixing up compass errors: ANDS is for acceleration/deceleration, not for turns.
Thinking all glass-cockpit instruments fail together — modern aircraft have redundant power sources.
Study Tips
Draw diagrams of the pitot-static system and label what each instrument reads and from which source.
Memorize ANDS (Accelerate North, Decelerate South) and understand why it happens.
Create a failure scenario chart: "If X fails, which instruments are affected?"
Practice explaining carburetor icing conditions — temperature and humidity combinations.
Know your vacuum and electrical systems cold — which instruments are on which system.
FAA References
Pilot's Handbook of Aeronautical Knowledge (PHAK)
Chapter 7 — Aircraft Systems
Pilot's Handbook of Aeronautical Knowledge (PHAK)
Chapter 8 — Flight Instruments
Related Free Tools
Sample Questions
Test your knowledge with these representative questions from the FAA exam.
1. If the pitot tube becomes blocked during flight, which instrument(s) will be affected?
Explanation: The pitot tube provides ram air pressure only to the airspeed indicator. A pitot blockage affects only the ASI. The altimeter and VSI use static pressure only.
2. The first indication of carburetor icing in an aircraft with a fixed-pitch propeller is:
Explanation: Carburetor ice restricts airflow to the engine, causing a loss of power shown by a decrease in RPM with a fixed-pitch propeller. With a constant-speed propeller, the first indication is a drop in manifold pressure.
3. If the vacuum system fails, which instruments will be affected?
Explanation: The vacuum system powers the attitude indicator and heading indicator. The turn coordinator is electrically driven, providing backup attitude reference if the vacuum system fails.
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